460 = DYNAMICAL GEOLOGY. [Boox IL. 
The rate of growth of peat varies within wide limits. An in- 
teresting example of the formation and growth of peat-moss in the 
latter half of the seventeenth century is on record.* In the year 
1651 an ancient pine forest occupied a level tract of land among the 
hills in the west of Ross-shire. ‘The trees were all dead, and in a 
condition to be blown down by the wind. About fifteen years later 
every vestige of a tree had disappeared, the site being occupied by 
a spongy green bog into which a man would sink up to the arm-pits. 
Beiore the year 1699 it had become firm enough to yield good peat 
for fuel. In a moor in Hanover a layer of peat from 4 to 6 feet 
thick formed in about thirty years. Near the Lake of Constance a 
layer of 3 to 4 feet grew in 24 years. Among the Danish 
mosses a period of 250 to 300 years has been required to form a 
layer 10 feet thick. Much must depend upon the climate, slope, 
drainage and soil. Some EHuropean peat-mosses are probably of 
extreme antiquity, having begun to form soon after the surface was 
freed from the snow and ice of the glacial period. In the lower 
parts of these mosses traces of the arctic flora which then over- — 
spread so much of the continent are to be met with. Change of 
climate and likewise of drainage may stop the formation of peat, so 
that shrubs and trees spring up on the firm surface. 
Peat-mosses cover many thousand square miles of Europe and 
North America. About one-seventh of Ireland is covered with bogs, 
that of Allen alone comprising 238,500 acres, with an average depth 
of 25 feet. Where lakes are gradually converted into bogs, the 
marshy vegetation advances from the shores, and sometimes forms a 
matted treacherous green surface, beneath which the waters of the 
lake still lie. The decayed vegetable matter from the under part of 
this crust sinks to the bottom of the water, forming there a fine 
peaty mud, which slowly grows upward. Eventually, as the spongy 
covering spreads over the lake, a layer of brown muddy water 
may be left between the still growing vegetation above and the 
muddy deposit at the bottom. Heavy rains, by augmenting this 
intermediate watery layer, sometimes make the centre swell up 
until the matted skin of moss bursts, and a deluge of black mud 
pours into the surrounding country. Many disastrous examples 
of this kind have been witnessed in Ireland and Scotland. The 
inundated ground is covered permanently with a layer of black 
peaty earth. 
I’'rom the treacherous nature of their surface peat-mosses have 
frequently been the receptacles for bodies of men and animals that 
ventured upon them. As peat possesses great antiseptic power, these 
remains are usually in a state of excellent preservation. In Ireland 
the remains of the extinct large Inish elk (Megaceros Hibernicus) 
have been dug up from many of the bogs. Human. weapons, tools 
and ornaments have been recovered abundantly from peat-mosses ; 
likewise crannoges, or pile dwellings (constructed in the original 
1 Karl of Cromarty, Phil. Trans. xxvii, ; 

